( 610 ) 
Op\ (dp *) | 
É En (de). ie, 
Pete Np er 
& is with great approximation independent of temperature ’) ; 
v 
holds. 
ar 
its values for successive densities in the neighbourhood of the eritical 
density were read from a pv-graph of accurate isotherms just above the 
critical point. Hence these values hold, too, for the critical tempera- 
“d ) 
ture itself. The value of (55) can be deduced from data published 
coex.k 
d 
a short time ago *) viz: (5) = 1.820. Interpolation between the 
coex.k 
Op 
oT 
as the density for which equation (A) holds. 
In connection with the deduction of this value, however, it must 
be remembered that this method has already Jed repeatedly to a 
result for d), differing from that found from the diameter, and that 
the results obtained by the two methods deviate so far from each 
other that the difference cannot be attributed to errors of observation 
or calculation. The values obtained according to these two methods 
must therefore be regarded as experimental data differing in general 
from each other and each of them deduced in a certain way. For 
instance, Kersom *) found 0.00418 for the experimental critical volume - 
of carbon dioxide (expressed in the theoretical normal volume as 
unit) using the law of the diameter, and 0.004438 for the volume 
for which equation (A) holds. And KAMERLINGH Onnes and Kresom *) 
mention that BRINKMAN ®) found a similar difference in the case of 
carbon dioxide and. of methyl chloride, as Minis‘) did for ethyl 
aether, isopentane and normal pentane. These deviations ave such 
values of ( ) obtained from the isotherms gave in this way 0.509 
v0 
1) M. Puancx, Ann. d. Phys. (4). 15. 457. 1882. Keesom (Proc. Dec. 1901 
Comm. 75) mentions three proofs communicated to him by Prof. Van per WAALS. 
One of them can be found in VAN pER WAALS—KounstamM, Lehrbuch der Ther- 
modynamik. I, p. 35 and 36. 
2) cf. W. H. Kersom, Proc. Jan. 1904. Comm. N° 88, (pg. 54). Thesis for the 
doctorate, Amsterdam 1904. p. 86. 
5) Comm. 115, last page. 
ele: 
5) Proc. Febr. 1908. Comm. N°. 104a, see also H. KAMERLINGH Onnes and 
Miss T. C. JOLLES. Proc. Febr. 1907, Suppl. 14. 
6) G. H. BRINKMAN, Thesis for the doctorate, Amsterdam. 1904, p. 43, 
7) Minus, Journ. of phys. chem. 8, 594 and 635. 1904, 
